A developer for developing electrostatic images, comprising: 100 wt. parts of a toner comprising toner particles, and 0.01-3 wt. parts of silica powder which has a particle size of 0.006-0.2 micron and is not fixed to the surfaces of the toner particles; the toner particles comprising 100 wt. parts of colored resinous particles (A) and 0.05-5 wt. parts of silica powder comprising silica particles which have a particle size of 0.002-0.2 micron and have been embedded in the surfaces of the colored resinous particles by mechanical impact means.